Pipelines and pressure vessels that generally operate under high pressure are very common in industry. Such pipelines and pressure vessels are used to transport or store a large variety of pressurised gasses and fluids. Closure arrangements are commonly used to provide quick access to the interior of such fluid or gas handling systems. Before accessing these systems via a closure arrangement, it is generally known to depressurize the system by means of a main bleed valve.
Closure arrangements often comprise a flange formed around an opening at the end of a hub-shaped extension that extends from some part, such as a pipe, of the fluid or gas handling system. A covering or closing element, which forms a cap, referred for the purposes of this document at as a “head”, is securely attached over the flanged opening to provide a fluid-tight and pressure-tight seal when the closure arrangement is closed. The head is removable to provide access to the interior of the pressurized system via the opening in the flange of the hub.
The head can be secured onto the flanged opening of the hub by a variety of different ways. One way is simply to provide a series of corresponding bolt holes through the head and around the circumference of the flange so that individual bolts may be inserted through the corresponding holes and tightened. A gasket is provided between the head and the flange, and tightening of the bolts causes the circumference of the head to be pressed against the flange. Fully tightening all the bolts provides sufficient closing pressure to provide a seal at the gasket that is sufficient to prevent the escape of the pressurized fluid or gas. However, a disadvantage of such bolt type closures is the installation and removal of the individual bolts can be time consuming. This is particularly the case when there are a large number of bolts to install or remove.
Another common type of closure is often referred to as a screw type closure. In such closure arrangements the flange is provided with a threaded outer surface, and the head is provided with a corresponding threaded inner surface. To seal the closure arrangement, the head is screwed onto the flange. However, a disadvantage of screw type closures is that the head may be required to be rotated around several rotations in order to be screwed onto the flange. For large closure arrangements, the head can be very heavy, and therefore it can be very difficult for a user to screw the head onto or off the flange.
Another type of closure is a lug type closure. An example of a lug type closure arrangement 10 is shown in FIG. 1. This prior art closure is an early closure from GD Engineering.
The closure arrangement 10 comprises a hub 12 that is adapted to fit over a part, such as a pipe, of a fluid handling system. At the outer end of the hub 12 is a radially outwardly extending flange 14. The flange 14 is provided with four lugs 16 that project outwardly from the flange 14. The closure arrangement 10 also comprises a head 20 that is adapted to fit over the flange 14 of the hub 12. The head comprises four inwardly projecting lugs 22 that correspond in size to the lugs 16 on the flange 14.
In addition the closure arrangement 10 comprises a pressure release device 40. The pressure release device 40 comprises a pressure release screw 42 that is rotatably connected to a deflector plate 44. Attached to the deflector plate 44 is a locking pin 46 projecting from the deflector plate 44 in a direction parallel to the pressure release screw 42.
The pressure release screw 42 is adapted to be received in a vent bore 25 extending from the outside of the head 20 inside the closure arrangement 10. The locking pin 46 is adapted to be received in a locking bore 29 on the head 20 and a corresponding locking bore 19 on one of the lugs 16 on the flange 14. The locking bore 29 extends through the head 20 and is aligned with the locking bore on one of the lugs 16 on the flange 14 when the closure arrangement 10 is in a closed position. The locking bore 19 on the flange 14 extends partially into the lug 16.
To close the closure arrangement 10 the head 20 is oriented such that the lugs 22 on the head are at different angular positions to the lugs 16 on the flange. The head 20 is then pushed axially onto the flange 14 without the lugs 22 on the head 20 interfering with the lugs 16 on the flange 14. Once the lugs 22 of the head 20 have been pushed past the lugs 16 of the flange 14 in the inner axial direction, the head 20 is rotated around a predetermined angle such that the lugs 22 are located behind the lugs 16 of the flange 14. The lugs 16 of the flange 14 will then prevent axial moment of the head 20 in the outer direction, and the head 20 is thus held pressure-tight against the flange 14.
Once the head 20 is in the closed position the pressure release 40 device is used to lock the closure arrangement 10. To lock the closure arrangement 10 the user installs the pressure release device 40 onto the closure arrangement 10. The user aligns the pressure release screw 42 with the vent bore 25 and the locking pin with the locking bore 29 on the head 20. The user then tightens the pressure release screw 42, which will urge the entire pressure release 40 device towards the head 20. The pressure release screw 42 will seal the vent bore 25, and provide a pressure tight seal. Furthermore the pin 46 will extend through the bore 29 on the head and into the bore 19 on the flange. The pin 46 will thus prevent rotation of the head 20 and opening of closure arrangement 10 until the pressure warning release screw 42 is released. Thus, the closure arrangement 10 will be in a locked state and the closure arrangement 10 cannot be opened until the pressure release screw 42 is unscrewed.
Lug type closure arrangements 10 of this type are preferable to screw type closure arrangements as the head can be moved from an open position to a closed position by rotating the head through a partial turn, e.g. 45°. For large closure arrangements, this can greatly increase the ease of opening and closing of the closure arrangement.
When in a closed position, the lugs provided on the head 20 and the flange 14 are disposed opposite each other and internal the closure arrangement 10. They are therefore are obscured from the view of the user by the head 20 and the flange 14, and it may be difficult for the user to appreciate how far the head 20 needs to be rotated before is can be moved axially off the flange 14.
In order to open the head 20, it is first necessary to unlock the closure arrangement 10. Unscrewing the pressure release screw 42 so that the pin 46 clears at least the bore 19 on the flange, release the seal between the pressure release screw 42 and the vent bore 25. If there is considerable internal pressure the user will be warned in the form of noticeable escaping gas or fluid. Opening the vent bore 25 will vent any fluids or gas that are under residual pressure inside the system near the closure arrangement 10. The user can then remove the pressure release device 40 from the head 20, permitting the rotation of the head 20 relative to the hub 12. The vent bore 25 is not used for venting the pressure in the system, but merely as a safety device to warn of the presence of pressure in the system. It can also vent any small residual pressure to ensure pressure equalization across the closure before opening.
On opening the closure arrangement 10, and once the pressure release device 40 has been removed, the head 20 is rotated relative to the hub 12 to a position at which the lugs 22 provided on the head 20 are not aligned with the lugs 16 provided on the flange 14. As both sets of lugs are not visible to the user, it can be difficult to align the lugs in such a way, and the user can therefore struggle to align the lugs and remove the head 20 from the flange 14.
FIG. 2 shows another example of a lug type closure arrangement 50 by GD Engineering. The closure arrangement 60 is substantially similar to the closure arrangement 10 shown in FIG. 1 except that it is provided with a stepped lug 24 adjacent each lug 22 of the head 20, and also that a stop pin 18 provided on the flange 14.
The closure arrangement 60 shown in FIG. 2 is closed in the same way as the closure arrangement 10 of FIG. 1. The head 20 is first pushed axially onto the flange 14, and then rotated relative to the flange 14 such that the lugs 22 on the head 20 are located behind the lugs 16 on the flange 14. The pressure release device 40 is then installed to lock the closure arrangement 60.
However, the closure arrangement 60 is opened in a different way to the closure arrangement 10 shown in FIG. 1. To open the closure arrangement 60 the pressure release device 40 is first removed, and then the head 20 is rotated relative to the flange 14 until one of the lugs 22 contacts the stop pin 18. The stop pin 18 is located such that when the lugs 22 are rotated to contact it, the lugs 22 are no longer located behind a corresponding lug 16, but each of the stepped lugs 24 is still located behind a corresponding lug 16.
If there is sufficient residual pressure in the fluid handling system the head 20 will then be urged axially in an outward direction until the stepped lugs 24 contact the lugs 16. The head 20 will therefore have been partially pushed off the flange 14 by the pressure of the system. The residual pressure can then therefore be safely vented without the pressure causing the head 20 to fly off the flange 14. If the pressure inside the system is not sufficient to urge the head 20 outwards such that the stepped lugs 24 contact the lugs 16 on the flange 14, the head 20 can be moved manually sufficiently outwards.
The user then rotates the head 20 until the lugs 24 are no longer located behind the lugs 16. At this point the head 20 can be moved off the flange 14 without any of the lugs interfering with each other.
FIGS. 1 and 2 show closure arrangements that only comprise a head 20 and a hub 12. However, as discussed closure arrangements for fluid handling systems can be very large, and therefore the heads 20 of such closure arrangements can be extremely heavy. For large closure arrangements, mechanical actuating means may be required both to rotate the head 20 relative to the flange 14 and remove it from the hub 12. The lugs on both the head 20 and the hub 12, as well as the stop pin 18 are not visible to the user from the outside of the closure arrangement 10 when it is in a closed position. Therefore, it is possible the user will forcibly rotate the head 20 too far relative to the hub 12, causing a lug 22 to forcibly impinge on the stop pin 18, potentially damaging both the stop pin 18 and the lug 22.
Similarly, if the lugs 22, 24 on the head 20 are not properly aligned relative to the lugs 16 on the flange 14 before axial force is applied to the head 20 to urge it from the flange 14, the lugs 22, 24 will be forced against the lugs 16 on the flange 14. Applying a large amount of force to both sets of the lugs in this way, particularly if powerful mechanical actuating means are used, could lead to deformation and damage of the lugs.
Lug type closure arrangements can also comprise support means such as davit arms to support the head 20 when it is removed from the hub 12. Other configurations of lug type arrangements are possible, but lug type closures all relying on a sequence of rotational and translation movements of the head 20 relative to the hub 12, and are all associated with the problems of the sort encountered with the arrangements of FIGS. 1 and 2.
It is an object of the invention to mitigate the above problems associated with lug type closure arrangements.